Suggestions For A DAC

I ask your for your wisdom and comments on finding a good used DAC. With all the new technology coming fast and furious, it seems like there are alot of good deals out there on used DACs. Some that I am considering Cal Audio Alpha, Muse Model 2, Adcom GDA 600/700, Bel Canto. Are tube units as good as SS? Also, is 96k upsampling worth it? I listen to mostly jazz and my budget is around $500-$800. My current system is: McIntosh MA6450 integrated amp, MCD7008 changer and Boston Acoustic A-150 speakers.

Thanks in advance.

John